Think of Jennifer, or as we like to call her, "Jen." Jen of the dazzling smile, Jen of the gorgeous chin, Jen with her hair down, Jen tousled, Jen as Rachel, Jen with Brad; Jen without Brad, Jen with Vince, Jen at the Oscars, and, of course, Jen as a neuron in the medial part of the temporal lobe.

Maybe you missed that last Jen.

A few years ago, a UCLA neurosurgeon named Itzhak Fried, while operating on patients who suffer from debilitating epileptic seizures, discovered what he now calls the "Jennifer Aniston Neuron."

In brain surgery, patients are often kept fully conscious, even when they have a probe implanted in their heads. Brains don't hurt when they're open, and this is standard procedure; the doctor needs to map the area where there's going to be surgery, the patient needs to answer the doctor's questions.

Fried asked his patients if they wouldn't mind doing a little exploratory science while on the operating table, and a bunch of them said yes.

Jen Vs. Julia Roberts

So he showed them a set of photographs, and he noticed when they came to a picture of Jen, very often a particular neuron would begin to flash, multiple times. When he showed these same patients pictures of Julia Roberts or random (not famous) people, or animals, or places, the neuron was quiet. Back to Jen? Back came the flash. He found this Aniston-specific brain cell in a number of people, and he wondered, what is going on?

Well, a flashing neuron is no big deal. That's what brain cells do. When a brain cell receives signals from other parts of the brain, the energy builds up, almost like a rising tide, and if the pressure gets strong enough, there's a release, a break, that is literally an electric flash. Neuroscientists call this a "spike" and they can see it (or with a tiny microphone, hear it) in a living brain. That's what Fried and his colleagues saw at UCLA.

The curious part was that there's a particular neuron devoted to images of Jennifer Aniston.

Actually, Jen's not the only one. Since Fried reported his findings, other neurons have been found that flash only for Julia Roberts, or for Halle Berry, or for Kobe Bryant. It may be that certain very famous people literally occupy special places in our brains. The question is, how?

Well, here's a theory. Maybe the neuron flashing "Jennifer!" isn't acting alone. Maybe it's the beacon atop a summit of associated neurons, each of which is flashing little bits of Jen. After all, when I say Jennifer Aniston, what comes to mind? Her blue eyes. Her chin (I'm slayed by her chin), her hair of course, her voice, her laugh, her fictive romance with Ross on "Friends", her dresses at the Oscars, her marriage to Brad Pitt, the divorce, her movies. And more fundamentally, those Jen-parts are themselves built from rawer bits: the blue of her eyes, her smooth skin, her flowing hair, her facial patterns (especially chins), which are in turn made of even smaller bits: units of light, dark, color, shading, form. Those lower-down neurons are no doubt doing other things in my brain (blue-ing up skies, lakes, and other people's blue eyes) when they're not building Ms. Aniston, but when Aniston calls, they come.

Jen Isn't Singular; She's Plural

So when Dr. Fried showed his patients pictures of Jennifer, (or maybe if he just mentioned her name) that reference might have triggered not just one, but a cascade of neural firings. And this may be the brain's way of storing a memory. Jennifer is not a single neuron, she's a plural, or as MIT professor Sebastian Seung puts it, she's "hierarchical organization."

That neuron shouting "Jen!" is receiving signals from thousands, maybe tens of thousands, maybe hundreds of thousands of neurons down below. Each time, the pattern is a little different. Thinking about Jen in "Bruce Almighty" is one pattern. Thinking about Jen having twins (Is she? They keep telling us that, but it's never...) is another. Each recollection probably slightly different from the ones before, but everytime, because it's Jen we're thinking of, the neuron at the top of the pile always flashes "Jen!"

What Is A Memory?

There's a deeper idea here: that when we remember someone, anyone, maybe what we're doing is making a specific neural connections in our brain. In physiological terms, what is a memory? Sebastian Sueng thinks it's a particular pattern of brain cells.

One day, says Professor Seung, it will be possible to look into a person's brain, (mine, say) and if Seung sees a certain sequence of flashes in me, he might exclaim, "Ah! I recognize this. This is Robert thinking about Jennifer Aniston's chin!"

Oh come on, that seems next to impossible. The patterns are so fleeting, electrical, fast, and impossibly small, no one's going to read my mind any time soon. Seung says, not soon, maybe, but one day it will happen. "This kind of mind reading," he says, "would require knowing the 'neural code,' which you can picture as a huge dictionary. Each entry of the dictionary lists a distinct perception and its corresponding pattern of neural activity."

Like constellations in the sky, there's a specific pattern in me for Jen smiling, a different pattern for Jen saying "We were on a break!" (Or was that Ross?)

That, anyway, is the neuronal theory of memory.

But is there any way to test this theory? Do an experiment?

Well, not yet.

Scientists can, as Dr. Fried did, see a single neuron spiking. There are fancy machines, fMRI scans, that can take fuzzy pictures of whole neighborhoods of hundreds of thousands of neurons being active. But if we want to see a memory of Jennifer Aniston forming in my head, first as two, then four, then ten, then 50, then 100, then 1,000 neurons flashing messages to each other forming a pattern — that we can't see. We haven't the tools.

The way to do it, says Seung in his new book Connectome is we should build a brain map. This map should let us see each and every neuron in a bit of my brain, the bigger the neighborhood, the more we will see. One day Seung would like to map an entire human brain, that's 80 billion neurons with roughly a 100 trillion connections between them.

Are Women Wired Differently Than Men?

Is such a map possible? He thinks so. It wouldn't be easy to do, because each neuron is crunched near its neighbors, twisting and turning. Neurons are like spaghetti. They jumble and clump. But with enough money, enough computing power, we could build, says Seung, a "Connectome," a definitive map of a human brain. And once we have one, he thinks we would know many things. Like, for example:

How are women different from men? (Are we wired differently?)

What happens in a schizophrenic brain? An autistic brain?

How do we learn?

How do memories form?

How do we make decisions?

What happens when we dream? Create? Love? Hate?

Seung thinks a brain map is essential to understanding how a mind works.

But there are many neuroscientists who think he's wrong. Very wrong. A brain map, they say, wouldn't tell you how a brain remembers Jennifer Aniston, wouldn't let you see a memory form, wouldn't be the key to unlock our minds. It would be a huge waste of money.

The two camps are now furiously debating all over the world. On Monday, April 2, with Radiolab regular Carl Zimmer, I will be hosting a duel between MIT's Sebastian Seung and Anthony Movshan of New York University. The two will duke it out on the campus of Columbia University. We're going to be streaming it on our Radiolab site. To get you ready, I will do another post that explores why so many neuroscientists think a human brain map is a dangerous idea. Check back here on Monday.